Cutting strips, cutting die knives, cutting rules and the like



Nov. 19, 1968 O CUTTING STRIPS, CUT

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w Q A m United States Patent ice 3,411,208 Patented Nov. 19, 1968 3,411,208 CUTTING STRIPS, CUTTING DIE KNIVES, CUTTING RULES AND THE LIKE Eugen Olof Malm, Sandviken, Sweden, assignor to Sandvikens Jernverks Aktiebolag, Sandviken, Sweden Filed June 14, 1966, Ser. No. 557,428 Claims priority, application Sweden, June 14, 1965, 7,776/65 6 Claims. (Cl. 30-350) ABSTRACT OF THE DISCLOSURE A steel cutting strip is disclosed having a main strip portion of substantially uniform hardness throughout, which is readily deformable so that it may be bent to form corners of low radii, and a cutting edge integral with the main body portion and of much greater hardness, but also of substantially uniform hardness throughout. The cutting edge portion is connected to the main strip portion by a thin layer integral with both of said portions. With this arrangement the cutting edge is sufiiciently small to permit it to be bent without damage, even though it is extremely hard, and the bond to the main strip portion remains intact.

This invention relates to cutting strips which are provided with pre-sharpened and pre-hardened cutting edges, the term cutting strip generally being used herein to include cutting die knives, cutting rules and die steel strips of the types which are used to cut various materials, such as, textiles, leather, plastic sheets, paper, etc. Such cutting strips may be used without further sharpening or heat treating and may be bent to desired shapes to form finished cutting dies.

It is an object of the present invention to provide improved cutting strips of the above character. It is a further object to provide improved cutting knife and cutting die structures of a wide range of characteristics and configurations. It is a further object to provide for the above with cutter strips and cutter knives which are superior to those available in the past and which may be used without the difficulties which have been encountered with prior structures. These and other objects will be in part obvious and in part pointed out below.

With cutting strips, it is desirable to provide a sharp cutting edge of precise dimensions and characteristics, and to support the edge during use. For example, a clicker die is produced by bending the cutting knife strip to form a closed configuration and then interconnecting the ends. The die is then placed with its cutting edge upon the sheet material being cut and is pressed against the material to perform the cutting operation. In the past it has been recognized that there are definite limitations upon the angle or are through which pre-hardened strips could be bent, i.e., the hardened cutting edge imposed limitations upon the bending. It is an object of the present invention to provide great freedom with respect to the acceptable bending characteristics of cutting strips.

In accordance with the present invention, a strip of steel which has been pre-sharpened along one edge, which has been given substantially uniform hardness throughout, is subjected to an edge-hardening operation producing a hardened cutting edge strip which is of much greater hardness than the remainder of the knife. Furthermore, the hardened cutting edge strip is quite narrow, so that it extends only a short distance from the cutting, and it is of substantially uniform hardness throughout. Hence, the resulting cutting strip has two portions, each of which is of substantially uniform hardness throughout, and which are interconnected or bonded together at a relatively thin layer or zone. The main strip portion or body has the hardness of the original strip, and it may be bent or otherwise worked. The cutting edge strip is of the hardness desired for the cutting edge, and it is supported throughout by its interconnection with the main strip portion. The cutting edge strip is relatively small in cross section, so that it may be bent easily and without causing undue stress or cracking. The main strip portion is suffi ciently resilient to cause the structure to withstand relatively severe abuse without damage. That is, the main strip provides the desired support and rigidity, and yet it will absorb impact forces which might damage similar structures of the prior art.

Referring to the drawings, FIGURES 1 to 4 are enlarged cross sectional views of four cutting strips constituting embodiments of the invention.

Referring to FIGURE 1 of the drawings, a cutting strip has two plane side faces 11 and 12 and a cutting edge 13 positioned centrally between the panes of the side faces. The cutting edge is formed by the intersection of two plane cutting edge surfaces 14 and 15 which define the converging cutting edge portion 16 of the strip. The forepart of the converging cutting edge portion 16 is the cutting edge strip 17 which is of greater hardness than the main strip portion. The cutting edge portion 17 is connected to the main strip portion along the relatively thin zone represented in the drawing by a line and constituting a thin layer portion 18. This thin layer portion is generally a segment of a cylinder, the axis of the cylinder being substantially along the cutting edge 13, or along a line parallel thereto.

.In the embodiment of FIGURE 3, the cutting strip 30 has side faces 21 and 22, and has its cutting edge 23 eccentric, i.e., offset from the center plane of the strip toward the side face 21. The cutting edge is formed by the converging plane cutting edge surfaces 24 and 25 which are inclined approximately at the same angle with respect to their side faces, so that surface 25 is of greater width than surface 24. A layer portion 28 connects the cutting edge strip to the main strip portion.

In the embodiment of FIGURE 3, the cutting strip 30 has side faces 31 and 32 and a cutting edge 33 formed by surfaces 34 and 35 upon the cutting edge strip 38. A pair of upper converging surfaces 36 and 37 define the tapered edge portion 39 of the main strip portion to which cutting edge strip 38 is connected by the layer 38b. In the embodiment of FIGURE 4, the cutting strip 40 has side faces 41 and 42 and an eccentric cutting edge 43 upon a cutting edge strip 48 and formed by converging surfaces 44 and 45. An additional surface 46 provides an additional taper above surface and defines the top of the tapered edge of the main strip portion. A thin layer 47a interconnects the harder portion 48 to the portion 47.

The intermediate or interconnecting layer (18 in FIG. 1) forms a transition layer between the harder cutting edge portion and the main part of the knife. This transition layer often is at least partly softer than the main part of the knife. The depth of the transition layer measured in the same direction as t may be for instance tt and is often of the size order .1 mm.

The cutting strips may be of either alloyed or carbon steels, but illustratively are of carbon steels which contain: .5% to .8% of carbon, 15 to .7S% of silicone, and 15% to .75% of manganese, the content of silicone and manganese being usually less than .35 and .60% respectively.

One such steel contains: .5 to 6% carbon, .15 to 35% silicone and .4% to .6% manganese.

In producing the cutting strips, the strip is first hardened preferably by a complete bainite hardening process. When there is partial bainite hardening, the structure contains both bainite and tempered martensite, usually up to 50% martensite. After the above hardening, one or each edge of the strip is ground to form a cutting edge of the shape desired in the finished cutting strip. The cutting edge is then subjected to the edge-hardening process, suitably using high frequency induction heating. The side faces of the strip may then be decar-burized so as to increase the ductility for bending. The hardened cutting edge strip is spaced from the side faces and is not decarburized.

The cutting edge hardening is carried on in such a Way as to produce the physical structure shown in the drawings and described above, with each of the cutting strips including a hardened cutting edge strip. The transverse dimension or maximum thickness of the cutting edge strip has the dimension e, and the main strip portion has the thickness of d. Measured from the cutting edge along the center plane of the strip, the depth or width of the cutting edge strip is indicated at t, and the depth or Width of the tapered portion is indicated at s, and t is less than s. Hence, the cutting edge strip comprises only a portion of the tapered edge of the cutting strip and e is substantially less than (I. In practice, e is not greater than .85 of d, usually less than .6 of (I, and often not greater than .4 of a. The dimension t is of the order of .2 mm. to .5 mm., usually between .3 mm. and .5 mm.

The main strip portion is of substantially uniform hardness, which is the hardness of the entire strip prior to the cutting edge hardening. That hardness and the other particular characteristics of the steel are determined by the desired characteristics and the proposed use of the cutting strip. However, in general, the hardness of the main strip portion is of the order of 285 to 450 Vickers, preferably within the range of 300 to 420 Vickers. The hardness of the cutting edge strips is within the range of 480 to 720 Vickers. the hardness being determined by the use for which the cutting strip is intended. Such cutting strips for use in cutting paper having a hardness of the order of 540 to 660 Vickers, and of the order of 480 to 600 Vickers for use with textiles, leather, plastics and the like.

While it has been explained above that the hardness of the main strip portion is substantially uniform up to the interconnecting layer (18 in FIGURE 1), the heat treatment may produce some change in the hardness of the main strip portion adjacent the interconnecting layer. However, any such change in hardness is not significant, and in no case is it suflicient to interfere with the proper use and operation of the cutting strip. The interconnecting layer 18 and the interconnecting layers in the other embodiments have a thickness of the order of .1 mm., although that thickness may vary, depending upon the particular steel, the size and shape of the strip and the cutting edge and the other characteristics which are determined for each particular cutting strip.

In general, the cutting edge angle (e.g., between surfaces 14 and 15 in FIGURE 1) is of the order of 40 to 60, suitably 52 and 55 for other of the above uses.

This invention provides the advantage that the zone which is of greater hardness has a smaller thickness than the main strip portion. Hence, the cutting strip may be bent and otherwise worked without undue strain upon the hardened cutting edge strip. In effect, the cutting edge strip is of such small width and cross section that the cutting strip may be bent around much smaller radii than has been possible with prior cutting strips and knives. For example, a cutting strip of .7 mm. thickness can be bent around a minimum radius of .75 mm. Under normal circumstances the bending is cold. However, on exceptional occasions, the cutting strip may be heated, but not to a temperature to destroy the hardness of the cutting edge strip. It has been found that cutting die knives produced in accordance with the present invention may have their cutting edges creased laterally to produce code markings, without ruptures in the cutting edges. The above is possible because the hardened cutting edge strip is of such small cross section that it is not damaged by sharp bends, and the relatively soft metal adjacent and in the interconnecting layer is sufiiciently ductile to permit it to be deformed.

In practice the present invention can be applied to cutting die knives for paper, for example, with a cutting knife thickness of .7 mm. to 1.4 mm. and a height of 12.5 mm. to 50 mm. For leather, the thickness may be 1.4 mm. to 5 mm., with a height of 12 /2 to 50 mm. Dies produced from cutting strips of smaller thickness require frame supports, whereas dies produced from thick cutting strips may be stabilized by ties.

What is claimed is:

1. A cutting strip comprising a main strip portion with opposite longitudinal side faces and an integral cutting edge portion, said cutting edge portion having longitudinal surfaces which converge from said longitudinal side faces and intersect to form a sharp cutting edge, said cutting strip being an integral body of steel and being of a uniform hardness except for the longitudinal portion adjacent said sharp cutting edge, said hardness being such that said strip can be bent without exceeding the acceptable permissible compressive and tensile stresses, said sharp cutting edge and said longitudinal portion adjacent thereto having a uniform hardness throughout which is substantially greater than the hardness of the remainder of said cutting strip, said cutting strip including an interconnecting layer with a thickness of the order of .1 mm. positioned between said longitudinal portion adjacent said sharp cutting edge and the next adjacent portion of said cutting strip and providing the sole interconnection therebetween, said longitudinal portion adjacent said sharp cutting edge having a maximum cross-sectional dimension in the direction parallel to a line transverse to said side faces which is not greater than .6 of the maximum thickness dimension between said side faces, whereby said longitudinal portion adjacent said sharp cutting edge is subjected to substantially less elongation and compression stresses than the side portions of said main body portion When the cutting strip is bent.

2. A cutting strip as described in claim 1 wherein the maximum thickness of said cutting edge portion is not greater than .85 of the thickness of said main strip portion.

3. A cutting strip as described in claim 1 wherein the maximum thickness of said cutting edge portion is not greater than .4 of the thickness of said main strip portion.

4. A cutting strip as described in claim 1, wherein said cutting edge portion extends from said layer portion along the central plane of said cutting strip a distance of the order of .2 to .5 mm.

5. A cutting strip as described in claim 1 wherein said main strip portion has a hardness of the order of 280 to 450 Vickers and wherein the hardness of said cutting edge portion is of the order of 480 to 720 Vickers.

6. A cutting strip as described in claim 1 which is formed of carbon steel which contains: .5% to .8% of carbon; .15% to .75% of silicone; and .15% to .75% of manganese.

References Cited UNITED STATES PATENTS 1,011,938 12/1911 Gaisman 30346.54 1,850,902 3/1932 Thompson 30346.54 1,989,886 2/1935 Roth 148150 2,426,985 9/1947 Darmara 148150 X 2,786,788 3/1957 Anderson 148-39 X 2,713,902 7/ 1955 Biss 30-350 X ANDREW R. JUHASZ, Primary Examiner.

G. WEIDENFELD, Assistant Examiner. 

